The three-phase alternate-current winding of a linear motor comprises three linear motor lines laid like meanders that produce an electromagnetic moving field. For example, linear motors are used to drive a magnetic levitation transport system for long-distance express traffic.
The production and laying of the alternate-current winding of a linear motor is accomplished with a laying vehicle that is put onto the track way (DE 37 37 719 A1).
The length of a winding period is defined by the groove/tooth geometry of the inductor packages and nearly constant over the length of the track way beam. But over the entire length of the track way the inductor cannot be fabricated and/or mounted as a uniform body or with a uniform geometry, and moreover, fabrication tolerances do occur. Furthermore, the track way has interruptions which, for example, are due to butt joints at bridge structures, for setoff of differences in length between inner track and outer track or due to elongation compensators (to compensate for changes in temperature).
It is possible to consider deviations from nominal sizes in fabrication and laying of a winding, but only to such an extent as these deviations are exactly known from the very beginning on. Changes in length occurring at a point of discontinuity throughout the service life of a motor winding due to thermal expansion and dynamic loads lead to an expansion and compression load for winding heads in longitudinal track way direction.
Some examples for potential impacts of such loads are given below:
Adverse effect on functional stability with regard to operating current conductivity, operating and failure voltage strength and mechanical-geometric installation size accuracy.
Slight tolerances in length can be offset by the elastic properties of the winding heads or line. For example, this would be possible with ground level plate track ways having a length of up to 6 m. With greater lengths, the tolerances in length add-up and the motor winding cannot be fabricated continuously with a uniform size. Special measures would have to be taken in the winding guidance. It has also been contemplated to lay the motor winding with an expansion loop at a point of discontinuity for thermal and/or dynamic elongation offset. But it bears crucial disadvantages. Winding production is not possible continuously. A standstill of the assembly machine will occur at every point of discontinuity for cutting of line length and for assembly of line guidance. It entails more consumption of material (moving field line, clamps, fixing rails, etc.). In particular, a standstill of the laying machine at every point of discontinuity is extremely obstructive.